CONFIRMING EXPOSURE: PESTICIDES IN BLOOD AND URINE

Few studies have been done involving biological monitoring for environmental pesticide exposures, particularly among children. Analytical methods capable of detecting residues of pesticides in blood or urine are still quite limited. Only a few laboratories in the U.S. are capable of detecting low level exposures to some of these compounds accurately and precisely. In fact, only the persistent organochlorine pesticides, most of which are banned, are routinely measured in blood. A panel of 12 pesticide metabolites can be measured routinely in urine at the National Center for Environmental Health.[162] Most of the organophosphate pesticide residues, and as many as eleven herbicides can reportedly be measured in urine.[163] Yet there
are numerous pesticide active ingredients and degradation products that are not readily measurable in humans, or are not measurable at all. In the cases where the methodology exists to measure pesticides in humans, residues are frequently detected, and correlate with environmental exposure levels. It would be particularly helpful to have more data on the levels of pesticides in the blood and urine of farm children in comparison with children who do not live in agricultural regions.

Non-Farm Families

There is evidence that the levels of pesticides in house dust are correlated with levels of the same pesticides measured in human blood. This information is based primarily on a small study in Colorado in which positive correlations were found between pesticides in dust and pesticides in blood.[164] This study did not evaluate other routes of pesticide exposure including food, water, and air.

In the National Health and Nutrition Examination Survey (NHANES III, 1988–1994), a sample of over 900 adult volunteers from all regions of the country, ages 20 to 59, was recruited for sampling of a panel of pesticides in urine.8 Farm populations were not specifically examined in this study, and children were not sampled. Only about a dozen pesticides that are readily metabolized into water-soluble products and eliminated in urine could be measured. Metabolites of two organophosphate pesticides, chlorpyrifos and parathion, were detected in 82 percent and 41 percent respectively of the people tested. Both chlorpyrifos and parathion are major agricultural pesticides; chlorpyrifos is also registered for use in the home. Pentachlorophenol, a wood preservative, was also commonly found, detected in 64 percent of the people sampled, and a metabolite of p-dichlorobenzene, a carcinogenic pesticide used in mothballs and toilet deodorizers, was detected in the urine of 98 percent of people tested.[165] These findings indicate that low-level exposures to pesticides are extremely prevalent even in the adult general population of the United States.

All 197 children in an Arkansas community had detectable residues of pentachlorophenol in their urine at levels as high as 240 ppb. A metabolite of p-dichlorobenzene was also detected in 97 percent of the children. The herbicide 2,4-D was found in the urine of 20 percent of the children, even though it is extremely short lived in the body, implying that one out of five children was exposed to this pesticide shortly before their urine was collected for analysis.[9] This community was seen as fairly representative and not disproportionately exposed, implying that pesticide exposures are ubiquitous among children in the United States today.

Farm Families

There is evidence that farm families experience elevated levels of pesticide residues in their blood and urine:

A report from the Agricultural Health Study indicates that agricultural families can receive an absorbed dose of pesticides after application by a member of the family. The report used indoor air sampling, hand wipe sampling, serum, and urine monitoring to evaluate exposures to the family of one farmer applicator. The farmer applied carbaryl to pumpkins using a hand-cranked duster. His serum carbaryl levels rose by three-orders-of-magnitude following use of the pesticide, and the carbaryl metabolite was detectable in his urine. Urine metabolite measurements on the spouse and two children demonstrated a doubling of excretion of the carbaryl metabolite following application of the pesticide. These results were seen even in the absence of a quantifiable increased carbaryl concentration in indoor air or house dust.[166]

Residents living near fields sprayed with organophosphate pesticides had small reductions in plasma and whole blood levels of the neurotransmitter enzyme cholinesterase during spraying season compared with residents living further from the fields, and with their own cholinesterase levels off-season. At the same time, infirmary records indicated a significant increase in visits for certain symptoms on days when organophosphate pesticides were sprayed. Symptoms included respiratory problems, headache, and eye irritation.[130] These data indicate that exposures to organophosphate pesticide drift may result in quantifiable cholinesterase inhibition in nearby residents.

Preliminary results from the Agricultural Health Study reveal that elevated blood serum pesticide levels have been detected in some farm families. The hazardous pesticide dieldrin, which has been banned in the United States since 1987, was found at significantly elevated levels in the blood of all members of one of the six farm families sampled. Further investigation revealed persistently elevated levels of this pesticide in food samples on the farm, although all legal food uses of this pesticide were canceled in 1974. Other persistent pesticides identified in the blood of farm families included chlordane and trans-nonachlor.[167] This finding may have significant implications for all environmentally persistent pesticides. If the dieldrin is determined to come from persistently contaminated farm soil, then it is even more important to stop using environmentally persistent pesticides, clean up the contaminated soil, and consider the cumulative risks from use of these toxic chemicals in the past.

Farm children under age six in a fruit growing region of Washington State were tested for urinary dimethylthiophosphate (DMTP), a metabolite associated with exposure to the organophosphates azinphos-methyl and phosmet, two highly toxic agricultural pesticides not registered for use in the home. The testing compared 46 families with a member involved in pesticide application and whose residence was within 200 feet of an orchard with 13 families who had no members working in agriculture and who lived farther from orchards. DMTP was detected in 66 percent of the farm children at a median concentration four times higher than in comparison children. However, DMTP was also detected in approximately 40 percent of non-farm children.[12] The non-farm children may have been exposed from dietary sources, pesticide drift, or contaminated soil and dust in this agricultural region.

In this same study, younger children tended to have higher pesticide concentrations in their urine than older children, consistent with expectations about disproportionate exposure. Children living closer to an orchard also tended to have slightly higher pesticide residues in their urine. The habit of wearing work shoes inside the home also correlated with measured exposure among the children of pesticide applicators. The methodology in this study may have tended to underestimate exposures due to the limited panel of urinary metabolites evaluated. Thus this study proves that childhood exposure to agricultural pesticides in farm areas does occur and can be significant, but the limitations of the study make it difficult to use for actually quantifying total exposure.

Socio-Economic Factors

There is a consistent association between higher residues of organochlorine pesticides in blood serum and black race and lower social class.[168] No similar studies have been done of Latino farmworkers, but exposures are likely to be similarly elevated. Many farm workers are non-white and are known to bear a disproportionate burden of exposure.[169] These associations indicate yet another reason for concern over certain disproportionately exposed groups of children. Non-white poor children living in farm communities are the most likely to be impacted by pesticides and are the most likely to suffer from any potential health effects from this exposure.

Methods should be developed to measure levels of all pesticides used in our environment in both environmental media and in human tissues or urine. Such methods should be applied to farm children and other particularly exposed populations to quantify the total exposure among these groups.